Polymers, photoresist compositions and methods of forming photolithographic patterns

ABSTRACT

Polymers containing a unit having a particular acetal moiety and photoresist compositions containing such a polymer. Substrates coated with the photoresist compositions and methods of forming photolithographic patterns. The polymers, photoresist compositions, methods and coated substrates find particular applicability in the manufacture of semiconductor devices.

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Application No. 61/429,107, filed Dec. 31, 2010, theentire contents of which are incorporated herein by reference.

FIELD

The invention relates generally to the manufacture of electronicdevices. More specifically, this invention relates to polymers,photoresist compositions, coated substrates and to photolithographicmethods which allow for the formation of fine patterns using a negativetone development process.

BACKGROUND

In the semiconductor manufacturing industry, photoresist materials areused for transferring an image to one or more underlying layers, such asmetal, semiconductor and dielectric layers, disposed on a semiconductorsubstrate, as well as to the substrate itself. To increase theintegration density of semiconductor devices and allow for the formationof structures having dimensions in the nanometer range, photoresists andphotolithography processing tools having high-resolution capabilitieshave been and continue to be developed.

One approach to achieving nm-scale feature sizes in semiconductordevices is the use of short wavelengths of light, for example, 193 nm orless, during exposure of chemically amplified photoresists. Immersionlithography effectively increases the numerical aperture of the lens ofthe imaging device, for example, a scanner having a KrF or ArF lightsource. This is accomplished by use of a relatively high refractiveindex fluid (i.e., an immersion fluid) between the last surface of theimaging device and the upper surface of the semiconductor wafer. Theimmersion fluid allows a greater amount of light to be focused into theresist layer than would occur with an air or inert gas medium.

The theoretical resolution limit as defined by the Rayleigh equation isshown below:

$R = {k_{1}\frac{\lambda}{NA}}$where k₁ is the process factor, λ is the wavelength of the imaging tooland NA is the numerical aperture of the imaging lens. When using wateras the immersion fluid, the maximum numerical aperture can be increased,for example, from 1.2 to 1.35. For a k₁ of 0.25 in the case of printingline and space patterns, 193 nm immersion scanners would only be capableof resolving 36 nm half-pitch line and space patterns. The resolutionfor printing contact holes or arbitrary 2D patterns is further limiteddue to the low aerial image contrast with a dark field mask wherein thetheoretical limit for k₁ is 0.35. The smallest half-pitch of contactholes is thus limited to about 50 nm. The standard immersion lithographyprocess is generally not suitable for manufacture of devices requiringgreater resolution.

Considerable effort has been made to extend the practical resolutioncapabilities of positive tone development in immersion lithography fromboth a materials and processing standpoint. One such example involvesnegative tone development (NTD) of a traditionally positive-typechemically amplified photoresist. NTD is an image reversal techniqueallowing for use of the superior imaging quality obtained with brightfield masks for printing the critical dark field layers. NTD resiststypically employ a resin having acid-labile (or acid-cleavable) groupsand a photoacid generator. Exposure to actinic radiation causes thephotoacid generator to form an acid which, during post-exposure baking,causes cleavage of the acid-labile groups, giving rise to a polarityswitch in the exposed regions. As a result, a difference in solubilitycharacteristics is created between exposed and unexposed regions of theresist such that unexposed regions of the resist can be removed byparticular developers, typically organic developers such as ketones,esters or ethers, leaving behind a pattern created by the insolubleexposed regions. Such a process is described, for example, in U.S. Pat.No. 6,790,579, to Goodall et al. That document discloses a photoresistcomposition comprising an acid-generating initiator and a polycyclicpolymer containing recurring acid labile pendant groups along thepolymer backbone. The exposed areas can be selectively removed with analkaline developer or, alternatively, the unexposed regions can beselectively removed by treatment with a suitable nonpolar solvent fornegative tone development.

Certain problems can result when applying conventional 193 nmphotoresists to the NTD process. The developed photoresist pattern can,for example, demonstrate significant thickness loss as compared with thepre-exposed resist layer. This can give rise to pattern defectsresulting from complete erosion of portions of the resist pattern duringsubsequent etching. Thickness loss is believed to be caused by cleavageand loss of commonly employed bulky acid labile groups such as largetertiary alkyl ester groups from the resist layer. Thickness loss forconventional 193 nm photoresists which rely solely on such bulky acidlabile groups for polarity switching can be particularly problematic dueto the high content of such groups. The use of a thicker resist layermay not be a practical solution as other issues such as reduction in thedepth of focus and pattern collapse can then result. The occurrence ofpattern collapse when using typical 193 nm photoresists for NTD isbelieved to be exacerbated by the relatively high content of(meth)acrylic acid units generated in exposed regions of the photoresistfollowing cleavage of certain acid-labile groups from(meth)acrylate-based polymers especially where such groups are solelyresponsible for the polarity switch. The (meth)acrylic acid unitscontribute to poor adhesion on organic and Si-based inorganic substratesdue to the polarity mismatch between resist patterns and substrates.Another problem associated with the use in NTD of such conventionalphotoresists relying solely on the aforementioned bulky acid labilegroups for polarity switching is etch resistance reduction.

There is a continuing need in the art for improved polymers, photoresistcompositions and photolithographic methods for negative tone developmentwhich allow for the formation of fine patterns in electronic devicefabrication and which avoid or conspicuously ameliorate one or more ofthe foregoing problems associated with the state of the art.

SUMMARY

The photoresist compositions of the invention include a polymer formedin part from a monomer which includes a particular acetal moiety.Preferred compositions and methods of the invention can result inreduced thickness loss and improvement in pattern collapse margin,resolution and photospeed in photolithographic processing.

In accordance with the invention, polymers are provided. The polymerscomprise: a first unit formed from a monomer of the following generalformula (I):

wherein: R₁ represents hydrogen or a C₁ to C₃ alkyl group; R₂ representsa single bond or a C₁ to C₁₀ organic group; R₃ represents a hydrogenatom or a C₁ to C₁₀ organic group; R₄ each independently represents ahydrogen atom or a C₁ to C₁₀ organic group, those bonded to a commoncarbon atom together optionally forming a ring; and R₅ eachindependently represents a C₁ to C₁₀ organic group, together optionallyforming a ring; and a second unit comprising a lactone moiety.

In accordance with a further aspect of the invention, photoresistcompositions are provided. The photoresist compositions comprise: apolymer comprising a first unit formed from a monomer of the followinggeneral formula (I):

wherein: R₁ represents hydrogen or a C₁ to C₃ alkyl group; R₂ representsa single bond or a C₁ to C₁₀ organic group; R₃ represents a hydrogenatom or a C₁ to C₁₀ organic group; R₄ each independently represents ahydrogen atom or a C₁ to C₁₀ organic group, those bonded to a commoncarbon atom together optionally forming a ring; and R₅ eachindependently represents a C₁ to C₁₀ organic group, together optionallyforming a ring; and a photoacid generator.

Also provided are coated substrates. The coated substrates comprise asubstrate and a layer of a photoresist composition of the invention asdescribed herein over a surface of the substrate.

Also provided are electronic devices formed by the methods describedherein.

As used herein: “g” means grams; wt % means weight percent; “L” meansliter; “mL” means milliliter; “nm” means nanometer; “mm” meansmillimeter; “min” means minute; “h” means hour; “A” means Angstroms;“mol %” means mole percent; “Mw” means weight average molecular weight;and “Mn” means number average molecular weight; the articles “a” and“an” mean one or more.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to the followingdrawings, in which like reference numerals denote like features, and inwhich:

FIG. 1A-E illustrates a process flow for forming a photolithographicpattern in accordance with the invention.

DETAILED DESCRIPTION

Polymers

The polymers of the invention include a first unit formed from a monomerthat includes a moiety having a ring structure and an acetal group. Thetwo oxygen atoms and secondary carbon atom (“acetal secondary carbonatom”) bonded to the oxygen atoms, characteristic of the acetal group,form a portion of the ring structure. Bonded to this acetal secondarycarbon atom is a structure which can take the form of two groups pendantto the ring structure or which together with the acetal secondary carbonatom can take the form of a ring structure. The acetal secondary carbonatom together with the pendant group(s) are acid labile, undergoing aphotoacid-promoted deprotection reaction on exposure to activatingradiation and heat treatment. The resulting cleavage of the acetalsecondary carbon atom and pendant group(s) is believed to result in theformation of hydroxy groups with the former acetal oxygen atoms. Thiscauses the polymer to become less soluble in an organic solvent used todevelop the resist layer allowing for the formation of a negative-typeimage.

The polymer includes a first unit formed from a monomer of the followinggeneral formula (I):

In formula (I), R₁ represents hydrogen or a C₁ to C₃ alkyl group,typically hydrogen or methyl. R₂ represents a single bond or a C₁ to C₁₀organic group, for example, C₁ to C₁₀ or C₁ to C₆ alkylene, C₂ to C₁₀ orC₂ to C₆ alkenylene, C₃ to C₈ alicyclic, a C₂ to C₁₀ or C₂ to C₇ alkylester, or a C₂ to C₁₀ or C₂ to C₈ alkyl ether. R₃ represents hydrogen ora C₁ to C₁₀ organic group such as C₁ to C₁₀ or C₁ to C₆ alkyl, C₂ to C₁₀or C₂ to C₆ alkenyl. Each R₄ independently represents a hydrogen atom ora C₁ to C₁₀ organic group, for example, C₁ to C₁₀ or C₁ to C₆ alkyl,aldehyde, alkoxycarbonyl, benzyloxymethyl, phenylsulfonyloxymethyl ortosyloxymethyl. Those R₄ groups bonded to a common carbon atom togethercan optionally form a ring. Each R₅ independently represents a C₁ to C₁₀organic group such as a C₁ to C₁₀ or C₁ to C₆ alkyl or acetyloxy group,and together optionally form a ring such as a C₃ to C₆ or C₄ to C₆cycloalkyl ring. It shall be understood for purposes of the descriptionand claims that the various R groups as defined herein can optionally besubstituted, meaning that one or more hydrogen atom can be replaced byanother atom such as a halogen, for example, fluorine. The content ofthe first unit in the polymer, while dependent on the number and typesof different units making up the polymer, is typically from 30 to 60 mol%.

Without limitation, suitable monomers of formula (I) include thefollowing:

Suitable monomers of formula (I) can be synthesized using knowntechniques, for example, subjecting the corresponding polyalcohol, inwhich two hydroxyl groups are joined together in an acetal group, toesterification with acryloyl chloride, methacryloyl chloride,ethacryloyl chloride or propacryloyl chloride. Synthesis of2,2-dimethyl-1,3-dioxan-5-yl methacrylate (IPDOMA),2-(2,2-dimethyl-1,3-dioxan-5-yl)butyl methacrylate (IPTPMA) and2-(1,5-dioxaspiro[5,5]undecan-3-yl)butyl methacrylate (CHTPMA), forexample, is described below in the Examples. Additional suitablesynthesis techniques are described in U.S. Pat. No. 7,416,867B2 andinvolve subjecting the corresponding polyalcohol, in which two hydroxylgroups are joined in an acetal group, to esterification with(alkyl)acrylic acid or to transesterification with an (alkyl)acrylicester in the presence of an enzyme. Techniques for forming acetal groupsin a protection reaction with the corresponding alcohol can be carriedout, for example, as described by Levene and Tipson, J. Biological Chem,1936 p 731, Orgmikum, VEB Deutscher Verlag der Wissenschaften, 17thedition, Berlin 1988, p. 398 or Protective Groups in Organic Synthesis,Wuts and Greene, Wiley-Interscience; 4^(th) Edition, Oct. 30, 2006.

The polymer further includes a second unit formed from a monomercomprising a lactone moiety. The second unit is typically present in thepolymer in an amount of from 20 to 60 mol %. Suitable such lactonemoieties are known in the art and include, for example, those of thefollowing formulae:

wherein R₁ is as defined above as being chosen from hydrogen and C1 toC3 alkyl, preferably hydrogen or methyl. Suitable monomers for thesecond unit are commercially available and/or can be synthesized usingknown techniques.

Other suitable additional monomeric units for the polymer include, forexample, one or more of the following: monomeric units formed from amonomer comprising a moiety of formula (I) which is different from thefirst unit; monomeric units containing ethers, lactones or esters, suchas 2-methyl-acrylic acid tetrahydro-furan-3-yl ester, 2-methyl-acrylicacid 2-oxo-tetrahydro-furan-3-yl ester, 2-methyl-acrylic acid5-oxo-tetrahydro-furan-3-yl ester, 2-methyl-acrylic acid3-oxo-4,10-dioxa-tricyclo[5.2.1.02,6]dec-8-yl ester, 2-methyl-acrylicacid 3-oxo-4-oxa-tricyclo[5.2.1.02,6]dec-8-yl ester, 2-methyl-acrylicacid 5-oxo-4-oxa-tricyclo[4.2.1.03,7]non-2-yloxycarbonylmethyl ester,acrylic acid 3-oxo-4-oxa-tricyclo[5.2.1.02,6]dec-8-yl ester,2-methyl-acrylic acid 5-oxo-4-oxa-tricyclo[4.2.1.03,7]non-2-yl ester,and 2-methyl-acrylic acid tetrahydro-furan-3-yl ester; monomeric unitshaving polar groups such as alcohols and fluorinated alcohols, such as2-methyl-acrylic acid 3-hydroxy-adamantan-1-yl ester, 2-methyl-acrylicacid 2-hydroxy-ethyl ester, 6-vinyl-naphthalen-2-ol, 2-methyl-acrylicacid 3,5-dihydroxy-adamantan-1-yl ester, 2-methyl-acrylic acid6-(3,3,3-trifluoro-2-hydroxy-2-trifluoromethyl-propyl)-bicyclo[2.2.1]hept-2-yl,and2-bicyclo[2.2.1]hept-5-en-2-ylmethyl-1,1,1,3,3,3-hexafluoro-propan-2-ol;monomeric units having acid labile moieties, for example, ester groupsthat contain a tertiary non-cyclic alkyl carbon such as t-butyl, or atertiary alicyclic carbon such as methyladamantyl or ethylfenchylcovalently linked to a carboxyloxygen of an ester of the polymer,2-methyl-acrylic acid 2-(1-ethoxy-ethoxy)-ethyl ester, 2-methyl-acrylicacid 2-ethoxymethoxy-ethyl ester, 2-methyl-acrylic acid2-methoxymethoxy-ethyl ester, 2-(1-ethoxy-ethoxy)-6-vinyl-naphthalene,2-ethoxymethoxy-6-vinyl-naphthalene, and2-methoxymethoxy-6-vinyl-naphthalene. Suitable monomers for suchadditional units are commercially available and/or can be synthesizedusing known methods. Where the polymer is used in a photoresist in apositive tone development method, the polymer typically includes a unitformed from a monomer which is an acid-labile alkyl or alkyloxy(meth)acrylate such as those described above. The additional units aretypically present in the polymer in an amount of from 40 to 70 mol %.

For imaging at sub-200 nm wavelengths such as 193 nm, the polymer istypically substantially free (e.g., less than 15 mol %) of phenyl,benzyl or other aromatic groups where such groups are highly absorbingof the radiation. The polymer can contain repeat units that contain ahetero atom, particularly oxygen and/or sulfur, for example, one or morechosen from: heteroalicyclic units fused to the polymer backbone; fusedcarbon alicyclic units such as provided by polymerization of anorbornene group; and carbocyclic aryl units substituted with one ormore hetero-atom-containing (e.g., oxygen or sulfur) groups, forexample, hydroxy naphthyl groups.

Preferred polymers in accordance with the invention include, forexample, the following:

The weight average molecular weight M_(w) of the polymers of theinvention is typically less than 100,000, for example, from 5000 to50,000, more typically from 7000 to 30,000 or from 10,000 to 25,000.

Suitable polymers in accordance with the invention can readily besynthesized by persons skilled in the art using known methods andcommercially available starting materials. The polymers can besynthesized, for example, by first dissolving the polymerizablegroup-containing monomers in a suitable organic solvent, for example,tetrahydrofuran, dioxane, ethyl acetate, dimethyl formamide, propyleneglycol methyl ether acetate (PGMEA), methylene chloride, chloroform,acetone, methyl ethyl ketone or the like, and degassing. A radicalinitiator can be dissolved in a suitable solvent which is the same ordifferent from that used for the monomer dissolution, and then added tothe monomer solution. Suitable radical initiators include, for example,2,2′-azobisisobutyronitrile (AIBN), dimethyl2,2′-azobis(2-methylpropionate)(Vazo™ 601, DuPont),2,2′-azobis(2,4-dimethyl)valeronitrile (Vazo™ 52, DuPont) and2,2-azobis(2-methylbutane-nitrile) (Vazo™ 67, DuPont). A reaction vesselis charged with a solvent which is the same or different from that usedfor the monomer solution and is heated to a temperature of from 40 to140° C., typically from 70 to 80° C. The initiator solution can then beadded to the reaction vessel, and the monomer solution added in adrop-wise manner to the vessel. The reaction mixture can be cooled andslowly added to a rapidly stirred non-solvent for precipitation.Suitable non-solvents include, for example, water, alcohols, alkanes,ethers, and combinations thereof. The polymer is collected, optionallyrinsed with a small amount of non-solvent and dried. For furtherpurification, the polymer can be re-dissolved in a suitable solvent,precipitated and dried.

Photoresist Compositions

Preferred photoresist compositions of the invention when used to formvery fine patterns in a negative tone development process can provideimprovements in one or more of resolution, top loss, pattern collapse,focus latitude, exposure latitude, photospeed and defectivity ascompared with conventional positive-tone photolithographic techniques.Preferred photoresists can further provide geometrically uniform resistpatterns for lines and contact holes. The compositions described hereincan be used in dry lithography or immersion lithography processes.

A. Matrix Polymer

The photoresist compositions include a matrix polymer that includes afirst unit formed from a monomer of the general formula (I) as describedabove. The polymer can be a homopolymer formed from a monomer of formula(I), or preferably a copolymer containing one or more units in additionto that formed from the monomer of formula (I), such as the polymersdescribed above. The matrix polymer as part of a layer of thephotoresist composition undergoes a change in solubility in an organicdeveloper as a result of reaction with acid generated from the photoacidgenerator following softbake, exposure to activating radiation and postexposure bake.

The matrix polymer is present in the resist composition in an amountsufficient to obtain a uniform coating of desired thickness. Typically,the matrix polymer is present in the composition in an amount of from 70to 95 wt % based on total solids of the resist composition.

B. Photoacid Generator

The photosensitive composition further comprises a photoacid generator(PAG) employed in an amount sufficient to generate a latent image in acoating layer of the composition upon exposure to activating radiation.For example, the photoacid generator will suitably be present in anamount of from about 1 to 20 wt % based on total solids of thephotoresist composition. Typically, lesser amounts of the PAG will besuitable for chemically amplified resists as compared withnon-chemically amplified materials.

Suitable PAGs are known in the art of chemically amplified photoresistsand include, for example: onium salts, for example, triphenylsulfoniumtrifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfoniumtrifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfoniumtrifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate;nitrobenzyl derivatives, for example, 2-nitrobenzyl-p-toluenesulfonate,2,6-dinitrobenzyl-p-toluenesulfonate, and2,4-dinitrobenzyl-p-toluenesulfonate; sulfonic acid esters, for example,1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; diazomethane derivatives, forexample, bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane; glyoxime derivatives, for example,bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime; sulfonic acid esterderivatives of an N-hydroxyimide compound, for example,N-hydroxysuccinimide methanesulfonic acid ester, N-hydroxysuccinimidetrifluoromethanesulfonic acid ester; and halogen-containing triazinecompounds, for example,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine. One ormore of such PAGs can be used.

C. Solvent

Suitable solvents for the photoresist compositions of the inventioninclude, for example: glycol ethers such as 2-methoxyethyl ether(diglyme), ethylene glycol monomethyl ether, and propylene glycolmonomethyl ether; propylene glycol monomethyl ether acetate; lactatessuch as methyl lactate and ethyl lactate; propionates such as methylpropionate, ethyl propionate, ethyl ethoxy propionate andmethyl-2-hydroxy isobutyrate; Cellosolve esters such as methylCellosolve acetate; aromatic hydrocarbons such as toluene and xylene;and ketones such as acetone, methylethyl ketone, cyclohexanone and2-heptanone. A blend of solvents such as a blend of two, three or moreof the solvents described above also are suitable. The solvent istypically present in the composition in an amount of from 90 to 99 wt %,more typically from 95 to 98 wt %, based on the total weight of thephotoresist composition.

D. Other Components

The photoresist compositions can also include other optional materials.For example, the compositions can include one or more of actinic andcontrast dyes, anti-striation agents, plasticizers, speed enhancers,sensitizers, and the like. Such optional additives if used are typicallypresent in the composition in minor amounts such as from 0.1 to 10 wt %based on total solids of the photoresist composition.

A preferred optional additive of resist compositions of the invention isan added base, for example, a caprolactam, which can enhance resolutionof a developed resist relief image. Other suitable basic additivesinclude: alkyl amines such as tripropylamine and dodecylamine, arylamines such as diphenylamine, triphenylamine, aminophenol,2-(4-aminophenyl)-2-(4-hydroxyphenyepropane, and the like. The addedbase is suitably used in relatively small amounts, for example, from0.01 to 5 wt %, preferably from 0.1 to 2 wt %, based on total solids ofthe photoresist composition.

Surface active polymers can optionally be used as an additive in thephotoresist formulation in order to simplify the immersion lithographicprocess by avoiding the need for a top-coat layer over the resist layer.Top-coat layers are typically used to prevent resist components such asphotoacid generators from contaminating the imaging lens surface.Surface active polymer additives added to the photoresist formulationsmigrate to the surface during the coating process due to theirrelatively low surface free energy. The surface active polymer additivesshould have a lower surface free energy than the matrix polymer to allowthe surface active polymer to migrate to the surface. A typical surfacefree energy of the surface active polymer additives is from 10 to 40mJ/m². Suitable surface active polymers are known in the art andinclude, for example, those disclosed by Tsibouklis and Nevell (AdvancedMaterials, 2003, 15, pp. 647-650). Exemplary suitable polymer additivesinclude, for example, poly(n-butyl acrylate), poly(n-butylmethacrylate), poly(1-butyl acrylate), poly(1-butyl methacrylate),poly(diethyl siloxane), poly(vinyl butyrate), polytetrahydrofuran,poly(propylene glycol), poly(tetramethylene oxide) and fluorinatedpolymers. The one or more additive polymer typically may be present inthe photoresist composition in relatively small amounts and stillprovide effective results. The content of the additive polymer maydepend, for example, on whether the lithography is a dry orimmersion-type process. For example, the additive polymer lower limitfor immersion lithography is generally dictated by the need to preventleaching of the resist components. A higher additive polymer contentwill typically result in pattern degradation. The one or more polymeradditive is typically present in the compositions of the invention in anamount of from 0.1 to 10 wt %, more typically from 1 to 5 wt %, based ontotal solids of the photoresist composition. The weight averagemolecular weight of the additive polymer is typically less than 400,000,for example from 5000 to 50,000.

Preparation of Photoresist Compositions

The photoresists used in accordance with the invention are generallyprepared following known procedures. For example, a photoresistcomposition of the invention can be prepared by dissolving thecomponents of the photoresist in the solvent component. The desiredtotal solids content of the photoresist will depend on factors such asthe particular polymers in the composition, final layer thickness andexposure wavelength. Typically the solids content of the photoresistvaries from 1 to 10 wt %, more typically from 2 to 5 wt %, based on thetotal weight of the photoresist composition.

Photoresist compositions of the invention find particular applicabilityin negative-tone development processes such as described below, but canbe used in positive-tone development wherein exposed portions of thephotoresist layer are removed in developer solutions.

Negative Tone Development Methods

The invention further provides methods for forming a photoresist reliefimage and producing an electronic device using photoresists of theinvention. The invention also provides novel articles of manufacturecomprising substrates coated with a photoresist composition of theinvention. Processes in accordance with the invention will now bedescribed with reference to FIG. 1A-E, which illustrates an exemplaryprocess flow for forming a photolithographic pattern by negative tonedevelopment.

FIG. 1A depicts in cross-section a substrate 100 which may includevarious layers and features. The substrate can be of a material such asa semiconductor, such as silicon or a compound semiconductor (e.g.,III-V or II-VI), glass, quartz, ceramic, copper and the like. Typically,the substrate is a semiconductor wafer, such as single crystal siliconor compound semiconductor wafer, and may have one or more layers andpatterned features formed on a surface thereof. One or more layers to bepatterned 102 may be provided over the substrate 100. Optionally, theunderlying base substrate material itself may be patterned, for example,when it is desired to form trenches in the substrate material. In thecase of patterning the base substrate material itself, the pattern shallbe considered to be formed in a layer of the substrate.

The layers may include, for example, one or more conductive layers suchas layers of aluminum, copper, molybdenum, tantalum, titanium, tungsten,alloys, nitrides or silicides of such metals, doped amorphous silicon ordoped polysilicon, one or more dielectric layers such as layers ofsilicon oxide, silicon nitride, silicon oxynitride, or metal oxides,semiconductor layers, such as single-crystal silicon, and combinationsthereof. The layers to be etched can be formed by various techniques,for example, chemical vapor deposition (CVD) such as plasma-enhancedCVD, low-pressure CVD or epitaxial growth, physical vapor deposition(PVD) such as sputtering or evaporation, or electroplating. Theparticular thickness of the one or more layers to be patterned 102 willvary depending on the materials and particular devices being formed.

Depending on the particular layers to be etched, film thicknesses andphotolithographic materials and process to be used, it may be desired todispose over the layers 102 a hard mask layer 104 and/or a bottomantireflective coating (BARC) 106 over which a photoresist layer 108 isto be coated. Use of a hard mask layer 104 may be desired, for example,with very thin resist layers, where the layers to be etched require asignificant etching depth, and/or where the particular etchant has poorresist selectivity. Where a hard mask layer is used, the resist patternsto be formed can be transferred to the hard mask layer which, in turn,can be used as a mask for etching the underlying layers 102. Suitablehard mask materials and formation methods are known in the art. Typicalmaterials include, for example, tungsten, titanium, titanium nitride,titanium oxide, zirconium oxide, aluminum oxide, aluminum oxynitride,hafnium oxide, amorphous carbon, silicon oxynitride and silicon nitride.The hard mask layer 104 can include a single layer or a plurality oflayers of different materials. The hard mask layer can be formed, forexample, by chemical or physical vapor deposition techniques.

A bottom antireflective coating 106 may be desirable where the substrateand/or underlying layers would otherwise reflect a significant amount ofincident radiation during photoresist exposure such that the quality ofthe formed pattern would be adversely affected. Such coatings canimprove depth-of-focus, exposure latitude, linewidth uniformity and CDcontrol. Antireflective coatings are typically used where the resist isexposed to deep ultraviolet light (300 nm or less), for example, KrFexcimer laser light (248 nm) or ArF excimer laser light (193 nm). Theantireflective coating 106 can comprise a single layer or a plurality ofdifferent layers. Suitable antireflective materials and methods offormation are known in the art. Antireflective materials arecommercially available, for example, those sold under the AR™ trademarkby Rohm and Haas Electronic Materials LLC (Marlborough, Mass. USA), suchas AR™ 40A and AR™ 124 antireflectant materials.

A photoresist composition as described herein is applied on thesubstrate over the antireflective layer 106 (if present) to form aphotoresist layer 108. The photoresist composition can be applied to thesubstrate by spin-coating, dipping, roller-coating or other conventionalcoating technique. Of these, spin-coating is typical. For spin-coating,the solids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific coating equipmentutilized, the viscosity of the solution, the speed of the coating tooland the amount of time allowed for spinning. A typical thickness for thephotoresist layer 108 is from about 500 to 3000 Å.

The photoresist layer can next be softbaked to minimize the solventcontent in the layer, thereby forming a tack-free coating and improvingadhesion of the layer to the substrate. The softbake can be conducted ona hotplate or in an oven, with a hotplate being typical. The softbaketemperature and time will depend, for example, on the particularmaterial of the photoresist and thickness. Typical softbakes areconducted at a temperature of from about 90 to 150° C., and a time offrom about 30 to 90 seconds.

The photoresist layer 108 is next exposed to activating radiation 110through a first photomask 112 to create a difference in solubilitybetween exposed and unexposed regions. References herein to exposing aphotoresist composition to radiation that is activating for thecomposition indicates that the radiation is capable of forming a latentimage in the photoresist composition. The photomask has opticallytransparent and optically opaque regions 113, 114 corresponding toregions of the resist layer to remain and be removed, respectively, in asubsequent development step for a positive-acting material asillustrated. The exposure wavelength is typically sub-400 nm, sub-300 nmor sub-200 nm, with 248 nm and 193 nm being typical. The methods finduse in immersion or dry (non-immersion) lithography techniques.

The exposure energy is typically from about 10 to 80 mJ/cm², dependentupon the exposure tool and the components of the photosensitivecomposition.

As shown in FIG. 1B, the exposed resist layer is made up of unexposedand exposed regions 108 a, 108 b. Following exposure of the photoresistlayer 108, a post-exposure bake (PEB) is performed. The PEB can beconducted, for example, on a hotplate or in an oven. Conditions for thePEB will depend, for example, on the particular photoresist compositionand layer thickness. The PEB is typically conducted at a temperature offrom about 80 to 150° C., and a time of from about 30 to 90 seconds.

The exposed photoresist layer is next developed to remove unexposedregions 108 a, leaving exposed regions 108 b forming a resist pattern asshown in FIG. 1C. The developer is typically an organic developer, forexample, a solvent chosen from ketones, esters, ethers, hydrocarbons,and mixtures thereof. Suitable ketone solvents include, for example,acetone, 2-hexanone, 5-methyl-2-hexanone, 2-heptanone, 4-heptanone,1-octanone, 2-octanone, 1-nonanone, 2-nonanone, diisobutyl ketone,cyclohexanone, methylcyclohexanone, phenylacetone, methyl ethyl ketoneand methyl isobutyl ketone. Suitable ester solvents include, forexample, methyl acetate, butyl acetate, ethyl acetate, isopropylacetate, amyl acetate, propylene glycol monomethyl ether acetate,ethylene glycol monoethyl ether acetate, diethylene glycol monobutylether acetate, diethylene glycol monoethyl ether acetate,ethyl-3-ethoxypropionate, 3-methoxybutyl acetate,3-methyl-3-methoxybutyl acetate, methyl formate, ethyl formate, butylformate, propyl formate, ethyl lactate, butyl lactate and propyllactate. Suitable ether solvents include, for example, dioxane,tetrahydrofuran and glycol ether solvents, for example, ethylene glycolmonomethyl ether, propylene glycol monomethyl ether, ethylene glycolmonoethyl ether, propylene glycol monoethyl ether, diethylene glycolmonomethyl ether, triethylene glycol monoethyl ether and methoxymethylbutanol. Suitable amide solvents include, for example,N-methyl-2-pyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.Suitable hydrocarbon solvents include, for example, aromatic hydrocarbonsolvents such as toluene and xylene. In addition, mixtures of thesesolvents, or one or more of the listed solvents mixed with a solventother than those described above or mixed with water can be used. Ofthese, 2-heptanone and 5-methyl-2-hexanone are particularly preferred.Other suitable solvents include those used in the photoresistcomposition.

The solvent can be present in the developer as a substantially purematerial, for example, in an amount greater than 95 wt %, greater than98 wt % or greater than 99 wt %, based on the total weight of thedeveloper. In the case a mixture of solvents are used in the developer,the boiling points of the solvents are preferably similar. The solventsof the developer are typically present in an amount of from 50 wt % to100 wt %, more typically from 80 wt % to 100 wt %, based on the totalweight of the developer.

The developer material may include optional additives, for example,surfactants such as described above with respect to the photoresist.Such optional additives typically will be present in minorconcentrations, for example, in amounts of from about 0.01 to 5 wt %based on the total weight of the developer.

The developer can be applied to the substrate by known techniques, forexample, by spin-coating or puddle-coating. The development time is fora period effective to remove the unexposed regions of the photoresist,with a time of from 5 to 30 seconds being typical. Development istypically conducted at room temperature. The development process can beconducted without use of a cleaning rinse following development. In thisregard, it has been found that the development process can result in aresidue-free wafer surface rendering such extra rinse step unnecessary.

The BARC layer 106, if present, is selectively etched using resistpattern 108 b as an etch mask, exposing the underlying hardmask layer104. The hardmask layer is next selectively etched, again using theresist pattern 108 b as an etch mask, resulting in patterned BARC andhardmask layers 106′, 104′, as shown in FIG. 1D. Suitable etchingtechniques and chemistries for etching the BARC layer and hardmask layerare known in the art and will depend, for example, on the particularmaterials of these layers. Dry-etching processes such as reactive ionetching are typical. The resist pattern 108 b and patterned BARC layer106′ are next removed from the substrate using known techniques, forexample, oxygen plasma ashing.

Using the hardmask pattern 104′ as an etch mask, the one or more layers102 are selectively etched. Suitable etching techniques and chemistriesfor etching the underlying layers 102 are known in the art, withdry-etching processes such as reactive ion etching being typical. Thepatterned hardmask layer 104′ can next be removed from the substratesurface using known techniques, for example, a dry-etching process suchas reactive ion etching. The resulting structure is a pattern of etchedfeatures 102′ as illustrated in FIG. 1E. In an alternative exemplarymethod, it may be desirable to pattern the layer 102 directly using theresist pattern 108 b without the use of a hardmask layer 104. Whetherdirect patterning is employed will depend on factors such as thematerials involved, resist selectivity, resist pattern thickness andpattern dimensions.

The negative tone development methods of the invention are not limitedto the exemplary methods described above. For example, the photoresistcompositions of the invention can be used in a negative tone developmentdouble exposure method for making contact holes. An exemplary suchprocess is a variation of the technique described with reference to FIG.1, but using an additional exposure of the photoresist layer in adifferent pattern than the first exposure. In this process, thephotoresist layer is exposed to actinic radiation through a photomask ina first exposure step. The photomask includes a series of parallel linesforming the opaque regions of the mask. Following the first exposure, asecond exposure of the photoresist layer is conducted through a secondphotomask that includes a series of lines in a direction perpendicularto those of the first photomask. The resulting photoresist layerincludes unexposed regions, once-exposed regions and twice-exposedregions.

Following the second exposure, the photoresist layer is post-exposurebaked and developed using a developer as described above. Unexposedregions corresponding to points of intersection of the lines of the twomasks are removed, leaving behind the once- and twice-exposed regions ofthe resist. The resulting structure can next be patterned as describedabove with reference to FIG. 1. This method is particularly suited toformation of contact holes in the manufacture of electronic devices.

EXAMPLES Matrix Polymer Synthesis

The following monomers were employed in the syntheses of copolymers inthe examples below:

Synthesis of 2,2-dimethyl-1,3-dioxan-5-yl methacrylate (IPDOMA)

2-amino-2-(hydroxymethyl)propane-1,3-diol hydrochloride (320 g, 2.03mol), 2,2-dimethoxypropane (240 g, 2.30 mol), and p-toluenesulfonic acidmonohydrate (16.2 g, 102 mmol) were combined into anhydrousdimethylformamide (1.0 L). The solution was stirred vigorously by amechanical stirrer for 48 hours at room temperature. Triethyl amine (300mL) and ethyl acetate (1.5 L) were added. A white precipitate formedimmediately. The white salt was filtered off and the low boiling pointsolvents were removed by a rotary evaporator. The product,(5-amino-2,2-dimethyl-1,3-dioxan-5-yl)methanol, was obtained bydistillation (250 g, 76%), by 107° C./0.3 torr. ¹H NMR (300 MHz, CDCl₃)δ1.48 (s, 3H), 1.53 (s, 3H), 3.14 (br, 2H), 3.51 (s, 1H), 3.53 (d, 2H),3.78 (d, 2H).

To a water (1.5 L) solution of(5-amino-2,2-dimethyl-1,3-dioxan-5-yl)methanol (251 g, 1.57 mol) andKH₂PO₄ (213 g, 1.57 mol) at 0° C., a water solution (1.8 L) of NaIO₄(336 g, 1.57 mol) was added dropwise. The reaction mixture was stirredat 0° C. for 2 hours and room temperature overnight. The product wasextracted by CH₂Cl₂ (5×300 mL), dried over MgSO₄ and distilled, yielding2,2-Dimethyl-1,3-dioxan-5-one (153 g, 75%) as a colorless liquid, by102° C./40 torr. ¹H NMR (300 MHz, CDCl₃) δ1.26 (s, 6H), 3.96 (s, 4H).

An anhydrous diethyl ether solution (250 mL) of2,2-Dimethyl-1,3-dioxan-5-one (35.5 g, 0.27 mol) was bubbled by nitrogenat 0° C. for 30 minutes. THF solution of LiAlH₄ (1M, 300 mL, 0.3 mol)was added dropwisely over 30 minutes. This solution was stirredovernight. Distilled water (75 mL) was added very carefully at 0° C. tothis solution. Crude product was extracted by CH₂Cl₂ (3×150 mL) anddried over MgSO₄. The solvent was removed. Product,2,2-dimethyl-1,3-dioxan-5-ol was purified by distillation, yielding theproduct as a colorless liquid (17.0 g, 48%). ¹H NMR (300 MHz, CDCl₃) δ1.48 (s, 3H), 1.51 (s, 3H), 2.80 (br, 1H), 3.55 (m, 1H), 3.71 (d, 1H),3.73 (m, 1H), 4.07 (d, 1H).

To a CH₂Cl₂ (200 mL) solution of 2,2-dimethyl-1,3-dioxan-5-ol (17.0 g,0.13 mol) at 0° C., triethylamine (20 mL) was added slowly. The reactionflask was flushed with nitrogen for 5 minutes. Methacryloyl chloride(13.5 g, 0.13 mol) was added dropwise. The reaction mixture was stirredat room temperature for 3 hours, then filtered, washed with a watersolution of NaHCO₃ (1M, 2×200 mL) and distilled water (2×200 mL). Thefiltrate was dried over MgSO₄. 1,4-hydroquinone (10 mg) was added as aninhibitor and solvent was removed. The oil was dissolved in ethylacetate (50 mL) and passed through a silica gel plug. Solvent wasremoved and the product was purified by distillation, yielding acolorless oil product (18.5 g, 71%). ¹H NMR (300 MHz, CDCl₃) δ 1.38 (s,3H), 1.41 (s, 3H), 1.92 (s, 3H), 3.77 (d, 1H), 3.82 (d, 1H), 4.05 (d,1H), 4.10 (d, 1H), 4.71 (m, 1H), 5.56 (s, 1H), 6.12 (s, 1H). ¹³C NMR(75.5 MHz, CDCl₃) δ 19.2, 20.6, 23.0, 61.6, 63.2, 99.3, 123.2, 124.5,138.1.

Synthesis of 2-(2,2-dimethyl-1,3-dioxan-5-yl)butyl methacrylate (IPTPMA)

In a 500 mL glass jar equipped with a magnetic stirring bar, 100 g oftris-(1,1,1-hydroxymethyl)-propane and 0.050 g of p-toluenesulfonic acidwere dissolved in 100 mL of acetone stirred overnight. The acetone wasremoved by distillation and the residue was redissolved in 50 mL ofether, washed with 10% NaHCO₃ and then twice with a brine solution. Thecrude product was obtained by removal of the ether by distillation. Thecrude material was then distilled under vacuum (3-4 mm of Hg) at 68° C.to yield 81.82 g (62.6%) of(5-ethyl-2,2-dimethyl-1,3-dioxan-5-yl)methanol as a clear oil: ¹H NMR(400 MHz, CDCl₃) δ 3.75 (d, J=5.5 Hz, 2H), 3.71-3.57 (m, 4H), 1.65 (t,J=5.5 Hz, 2H), 1.42 (s, 2H), 1.39 (s, 2H), 1.36-1.25 (m, 2H), 0.85 (t,J=7.6 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 98.12, 65.20, 63.22, 36.96,27.13, 23.88, 20.34, 7.01.

In a glovebox, 20 g of (5-ethyl-2,2-dimethyl-1,3-dioxan-5-yl)methanolalong with 32 mL of triethyl amine was dissolved in 100 mL of dryCH₂Cl₂. A solution of 13.5 mL methacryloyl chloride in 20 mL CH₂Cl₂ wasthen slowly added to the initial solution and stirred overnight. Thesolution was removed from the glovebox, 10 mL of methanol was added, andthe solution was stirred for 10 min. The solution was washed twice withbrine, dried over MgSO₄, and the crude material was recovered by removalof the solvent under vacuum. The crude product was then passed through asilica plug using ether and dried to yield 20.2 g of the final product(72.6%): ¹H NMR (400 MHz, CDCl₃) δ 6.13-6.00 (m, 1H), 5.64-5.43 (m, 1H),4.38-4.18 (m, 2H), 3.79-3.45 (m, 4H), 1.94 (dd, J=1.5, 1.0 Hz, 3H),1.53-1.22 (m, 7H), 1.00-0.69 (m, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 167.04,135.96, 125.88, 110.25, 73.19, 66.05, 64.75, 36.32, 34.91, 25.08, 23.92,23.77, 18.24.

Synthesis of 2-(1,5-dioxaspiro[5.5]undecan-3-yl)butyl methacrylate(CHTPMA)

CHTPMA was prepared using a similar reaction scheme as described forIPTPMA except that cyclohexanone was used instead of acetone to protectthe tris-(1,1,1-hydroxymethyl)-propane.

Synthesis of poly(IPDOMA/OTDA)

Monomers of IPDOMA (18.01 g) and OTDA (19.99 g) were dissolved in 57.0 gof PGMEA. The monomer solution was then degassed by bubbling withnitrogen for 20 min. A 500 mL three-neck flask equipped with a condenserand a mechanical stirrer was charged with PGMEA (28.9 g) and the solventwas degassed by bubbling with nitrogen for 20 min and subsequentlybrought to a temperature of 80° C. V601 (2.071 g) was dissolved in 7.6 gof PGMEA and the initiator solution was degassed by bubbling withnitrogen for 20 min. The initiator solution was added into the reactionflask and then monomer solution was fed into the reactor dropwise overthe 3 hour period under rigorous stirring and nitrogen environment.After monomer feeding was complete, the polymerization mixture was leftstanding for an additional hour at 80° C. After a total of 4 hours ofpolymerization time (3 hours feeding and 1 hour post-feeding stirring),the polymerization mixture was allowed to cool down to room temperature.Precipitation was carried out in MTBE (1500 g). The powder precipitatedwas filtered, air-dried overnight, re-dissolved in 75 g of THF, andre-precipitated into MTBE (1500 g). The final polymer was collected byfiltration, air-dried overnight and further dried under vacuum at 60° C.for 48 hours to give 26.98 g (Mw=21,414 and Mw/Mn=2.77) of the following“Polymer A”:

Synthesis of poly(IPTPMA/OTDA)

Monomers of IPTPMA (20.86 g) and OTDA (19.136 g) were dissolved in 60 gof PGMEA. The monomer solution was then degassed by bubbling withnitrogen for 20 min. A 500 mL three-neck flask equipped with a condenserand a mechanical stirrer was charged with PGMEA (29.96 g) and thesolvent was degassed by bubbling with nitrogen for 20 min andsubsequently brought to a temperature of 80° C. V601 (1.983 g) wasdissolved in 8 g of PGMEA and the initiator solution was degassed bybubbling with nitrogen for 20 min. The initiator solution was added intothe reaction flask and then monomer solution was fed into the reactordropwise over the 3 hour period under rigorous stirring and nitrogenenvironment. After monomer feeding was complete, the polymerizationmixture was left standing for an additional hour at 80° C. After a totalof 4 hours polymerization time (3 hours feeding and 1 hour post-feedingstirring), the polymerization mixture was allowed to cool down to roomtemperature. Precipitation was carried out in MTBE (1650 g). The powderprecipitated was filtered, air-dried overnight, re-dissolved in 120 g ofTHF, and re-precipitated into MTBE (1650 g). The final polymer wascollected by filtration, air-dried overnight and further dried undervacuum at 60° C. for 48 hours to give 32.2 g (Mw=13,198 and Mw/Mn=1.84)of the following “Polymer B”:

Synthesis of poly(CHTPMA/OTDA)

Monomers of CHTPMA (22.38 g) and OTDA (17.62 g) were dissolved in 60 gof PGMEA. The monomer solution was then degassed by bubbling withnitrogen for 20 min. A 500 mL three-neck flask equipped with a condenserand a mechanical stirrer was charged with PGMEA (29.592 g) and thesolvent was degassed by bubbling with nitrogen for 20 min andsubsequently brought to a temperature of 80° C. V601 (1.825 g) wasdissolved in 8 g of PGMEA and the initiator solution was degassed bybubbling with nitrogen for 20 min. The initiator solution was added intothe reaction flask and then monomer solution was fed into the reactordropwise over the 3 hour period under rigorous stirring and nitrogenenvironment. After monomer feeding was complete, the polymerizationmixture was left standing for an additional hour at 80° C. After a totalof 4 hours polymerization time (3 hours feeding and 1 hour post-feedingstirring), the polymerization mixture was allowed to cool down to roomtemperature. Precipitation was carried out in MTBE (1650 g). The powderprecipitated was filtered, air-dried overnight, re-dissolved in 120 g ofTHF, and re-precipitated into MTBE (1650 g). The final polymer wascollected by filtration, air-dried overnight and further dried undervacuum at 60° C. for 48 hours to give 30.68 g (Mw=13,504 and Mw/Mn=1.74)of the following “Polymer C”:

In Table 1 are listed monomer compositions, GPC data (molecular weightsand distributions), and polymerization yields for the polymer examples.

TABLE 1 Polymer Example Composition Mw Mw/Mn Yield A IPDOMA/OTDA 21,4142.77 71% (50/50) B IPTPMA/OTDA 13,198 1.84 81% (50/50) C CHTPMA/OTDA13,504 1.74 77% (50/50) *Molar composition as a feed ratio in thepolymerizationAdditive Polymer Synthesis: Poly(n-BMA)

13.01 g of n-butyl methacrylate (n-BMA) was dissolved in 7 g of THF. Themixture was degassed by bubbling with nitrogen for 20 min. A 500 mLflask equipped with a condenser, nitrogen inlet and mechanical stirrerwas charged with 8 g of THF and the solution brought to a temperature of67° C. 2.11 g of V601 (10.0 mol % with respect to monomers) wasdissolved in 2 g of THF and charged into the flask. The monomer solutionwas fed into the reactor at a rate of 6.29 mL/h. The monomer feeding wascarried out for 3 hours 30 min. After monomer feeding was complete, thepolymerization mixture was stirred for an additional 30 min at 67° C.After a total of 4 hours polymerization time (3 hours 30 min feeding and30 min stirring), 7 g of THF was added to the reactor and thepolymerization mixture was cooled down to room temperature.Precipitation was carried out in 0.4 L of cold methanol. Afterfiltration, the polymer was dried in a vacuum oven at 60° C. for 48hours to give 8.4 g (Mw=12,284 and Mw/Mn=1.79) of the following“Additive A”:

Photoresist Composition Formulation

Example 1

2.624 g of Polymer A and 0.064 g of Additive A were dissolved in 29.040g of PGMEA, 19.360 g of cyclohexanone, and 48.400 g ofmethyl-2-hydroxyisobutyreate. To this mixture were added 0.480 g of PAGA and 0.032 g of 1-(tert-butoxycarbonyl)-4-hydroxypiperidine. Theresulting mixture was rolled on a roller for six hours and then filteredthrough a Teflon filter having a 0.2 micron pore size.

Example 2

2.624 g of Polymer B and 0.064 g of Additive A were dissolved in 29.040g of PGMEA, 19.360 g of cyclohexanone, and 48.400 g ofmethyl-2-hydroxyisobutyreate. To this mixture were added 0.480 g of PAGA and 0.032 g of 1-(tert-butoxycarbonyl)-4-hydroxypiperidine. Theresulting mixture was rolled on a roller for six hours and then filteredthrough a Teflon filter having a 0.2 micron pore size.

Example 3

2.624 g of Polymer C and 0.064 g of Additive A were dissolved in 29.040g of PGMEA, 19.360 g of cyclohexanone, and 48.400 g ofmethyl-2-hydroxyisobutyreate. To this mixture were added 0.480 g of PAGA and 0.032 g of 1-(tert-butoxycarbonyl)-4-hydroxypiperidine. Theresulting mixture was rolled on a roller for six hours and then filteredthrough a Teflon filter having a 0.2 micron pore size.

Example 4

2.784 g of Polymer B and 0.064 g of Additive A were dissolved in 29.040g of PGMEA, 19.360 g of cyclohexanone, and 48.400 g ofmethyl-2-hydroxyisobutyreate. To this mixture were added 0.320 g of PAGA and 0.032 g of 1-(tert-butoxycarbonyl)-4-hydroxypiperidine. Theresulting mixture was rolled on a roller for six hours and then filteredthrough a Teflon filter having a 0.2 micron pore size.

Example 5

2.784 g of Polymer C and 0.064 g of Additive A were dissolved in 29.040g of PGMEA, 19.360 g of cyclohexanone, and 48.400 g ofmethyl-2-hydroxyisobutyreate. To this mixture were added 0.320 g of PAGA described above and 0.032 g of1-(tert-butoxycarbonyl)-4-hydroxypiperidine. The resulting mixture wasrolled on a roller for six hours and then filtered through a Teflonfilter having a 0.2 micron pore size.

Dry Lithographic Process and Contrast Evaluation

Examples 6-10

Dry lithographic processing was carried out for each of the photoresistcompositions of Examples 1-5 on 200 mm silicon wafers using a TELCleanTrack ACT 8 linked to an ASML/1100 scanner with a maximum numericalaperture (NA) of 0.75. Silicon wafers were spin-coated with AR™ 77bottom-antireflective coating (BARC) material (Rohm and Haas ElectronicMaterials) and baked for 60 seconds at 205° C. to yield a film thicknessof 840 Å. Photoresist compositions of Examples 1-5 were coated on theBARC-coated wafers and soft-baked at 90° C. for 60 seconds on a TELCleanTrack ACT 8 coater/developer to provide a resist layer thickness of900 Å.

The photoresist-coated wafers were then exposed through a blank maskusing 0.75 NA and a Quadrapole 30 illumination condition with 0.89 outersigma and 0.64 inner sigma. The exposure was carried out with a startingdose of 1.0 mJ/cm² in increments of 0.4 mJ/cm² to expose 100 die in a10×10 array on the wafer in a dose range from 1.0 to 40.6 mJ/cm². Theexposed wafers were post-exposure baked at various temperatures rangingfrom 85 to 120° C. for 60 seconds and then developed using 2-heptanonefor 10 seconds on a TEL CleanTrack ACT 8 coater/developer. The remainingfilm thickness for different exposure doses was measured on a ThermaWaveOptiprobe (KLA-Tencor) and NTD contrast curves were obtained by plottingremaining film thickness as a function of exposure energy. From thecontrast curves, the threshold energy (E_(th)) was determined as theminimum energy to reach constant film thickness and used as a measure ofphoto-sensitivity of each resist composition for NTD process. Theresults are shown in Table 2.

Examples 6-8 and 9-10 were run with PAG loadings of 15 wt % and 10 wt %,respectively, based on the total solids of the resist composition. NTDcontrast curves obtained from the examples were compared to see thedifference in contrast properties between the leaving group monomers(IPDOMA, IPTPMA and IPCHMA). At a 15 wt % PAG loading in Examples 6-8,the IPTPMA based formulation (Example 2) yielded a good NTD contrast forthe particular process conditions. The IPTPMA-containing formulationcomprising Polymer B started a solubility switch at ˜5 mJ/cm² andexhibited E_(th) values at 10.6 mJ/cm². The IPDOMA-containingformulation comprising Polymer A exhibited an instant polarity switcheven at the starting dose of 1.0 mJ/cm² and reached E_(th) under 2.0mJ/cm². Based on the results, it appears that IPDOMA monomer is aneffective leaving group monomer that requires a very low activationenergy for the chemically amplified deprotection reaction. TheCHTPMA-containing formulation containing Polymer C was completelydeveloped away, indicating a slower photospeed. When the post-exposurebake and PAG loading was adjusted as in Examples 9 and 10, the IPDOMA-and CHTPMA-containing formulations (Examples 4 and 5) exhibited goodcontrast with a high E_(th) value of 9.2 and 9.8 mJ/cm², respectively.

TABLE 2 Resist Matrix PAG Ex. Composition Polymer Loading* PEB Temp.E_(th) 6 Ex. 1 B 15 wt % 85° C. <2.0 mJ/cm²  7 Ex. 2 C 15 wt % 85° C.10.6 mJ/cm² 8 Ex. 3 D 15 wt % 100° C.  N/A* 9 Ex. 4 C 10 wt % 90° C. 9.2 mJ/cm² 10 Ex. 5 D 10 wt % 120° C.   9.8 mJ/cm² *E_(th) was notobserved up to 40.6 mJ/cm²Immersion Lithographic Process

Examples 11-12

300 mm silicon wafers were spin-coated with AR™ 40A antireflectant (Rohmand Haas Electronic Materials) to form a first bottom antireflectivecoating (BARC) on a TEL CLEAN TRAC LITHIUS i+ coater/developer. Thewafer was baked for 60 seconds at 215° C., yielding a first BARC filmthickness of 840 Å. A second BARC layer was next coated over the firstBARC using AR™ 124 antireflectant (Rohm and Haas Electronic Materials),and was baked at 205° C. for 60 seconds to generate a 200 Å top BARClayer. Photoresist formulations of Example 4 were then coated on thedual BARC-coated wafers and soft-baked at 90° C. for 60 seconds on a TELCLEAN TRACK LITHIUS i+ coater/developer to provide a resist layerthickness of 900 Å.

The photoresist-coated wafers were exposed through a mask on an ASMLTWINSCAN XT:1900i immersion scanner using two different illuminationconditions: (1) Annular illumination with 1.35 NA, 0.9 outer sigma, 0.7inner sigma and XY polarization (Example 11), and (2) Crossed sectoralquadruple (C-Quad) illumination with 1.35 NA, 0.9 outer sigma, 0.7 innersigma and XY polarization (Example 12). The exposed wafers werepost-exposure baked at 90° C. for 60 seconds and then developed using2-heptanone for 25 seconds on a TEL CLEAN TRACK™ LITHIUS™ i+coater/developer to give negative tone patterns. Critical dimensions(CDs) were measured on a Hitachi CG4000 CD SEM using a mask CD at 60 nm(the diameter of an opaque circle on the mask) and a pitch CD at 90 nm(a mask CD plus the distance between opaque circles) to compare theresolution capability of each formulation for ˜45 nm contact holes.

Immersion lithographic results are summarized in Table 3. Under bothconditions, the formulation exhibited good resolution for 45 nm holes at90 nm pitch with good pattern fidelity.

TABLE 3 Resist Ex. Composition Illumination PEB Temp. E_(s)* 11 Ex. 4Annular 90° C. 70.0 mJ/cm² 12 Ex. 4 C-Quad 90° C. 82.8 mJ/cm² *Exposureenergy to print 45 nm holes at 90 nm pitch **No resolution for 45 nmholes at 90 nm pitch

What is claimed is:
 1. A method of forming a photolithographic pattern,comprising: (a) providing a substrate comprising one or more layer to bepatterned over a surface of the substrate; (b) applying a layer of aphotoresist composition over the one or more layer to be patterned; (c)patternwise exposing the photoresist composition layer to actinicradiation; (d) heating the exposed photoresist composition layer in apost-exposure bake process; and (e) applying an organic developer to thephotoresist composition layer to remove a portion of the photoresistcomposition layer, thereby forming a photoresist pattern, whereinunexposed regions of the photoresist layer are removed by the developerto form the photoresist pattern; wherein the photoresist compositioncomprises: a polymer comprising a first unit formed from a monomer ofthe following general formula (I):

wherein: R₁ represents hydrogen or a C₁ to C₃ alkyl group; R₂ representsa single bond or a C₁ to C₁₀ organic group; R₃ represents a hydrogenatom or a C₁ to C₁₀ organic group; R₄ each independently represents ahydrogen atom or a C₁ to C₁₀ organic group, those bonded to a commoncarbon atom together optionally forming a ring; and R₅ together form aC₅ or C₆ monocyclic cycloalkyl group; and a photoacid generator.
 2. Themethod of claim 1, wherein the polymer further comprises a second unitcomprising a lactone moiety.
 3. The method of claim 2, wherein thepolymer further comprises a third unit comprising an ether, an ester, apolar group or an acid labile moiety, wherein the third unit isdifferent from the first unit and the second unit.
 4. The method ofclaim 1, wherein the polymer further comprises a second unit formed froma monomer which is an acid-labile alkyl or alkyloxy (meth)acrylate. 5.The method of claim 1, wherein the organic developer comprises a solventchosen from ketones, esters, ethers, hydrocarbons, and mixtures thereof.6. The method of claim 5, wherein the solvent is 2-heptanone or5-methyl-2-hexanone.
 7. The method of claim 1, wherein the solvent ispresent in the organic developer in an amount greater than 95 wt % basedon the total weight of the developer.